Support top-down 2-D movement in character controller

I'd like to set up a character controller for a top-down 2-D game. There would be no up vector. The controller would focus on maintaining separation between the character and walls, and possibly sliding along wall angles.

I'm not immediately sure how the existing support could be made to work with this. If I wanted a character to slide along walls, it seems like I could fake it in some circumstances. But then the character might get stuck if attempting to slide along a wall perpendicular to the unused up vector, resulting in slides in some situations but not others. Maybe that's inaccurate but it seems like it'd be true.

Thanks.